China is building its second aircraft carrier, the defence ministry said yesterday, as Beijing expands its naval capabilities amid maritime disputes with neighbours in the East and South China Seas.

"This aircraft carrier is being developed according to entirely domestic designs," defence ministry spokesman Yang Yujun told a regular briefing, adding it was under construction in Dalian, a northeastern port.

The official confirmation comes after months of rumours and hints from military officials.

Beijing has rapidly expanded its military in recent years, rattling its neighbours and attracting the attention of the United States, which is making a foreign policy "pivot" towards Asia.

China's first aircraft carrier, the Liaoning, is a secondhand Soviet ship built more than 25 years ago. It was commissioned in 2012 after extensive refits.

The new vessel will have a displacement of 50,000 tonnes and use "conventional power", Yang said, as opposed to being nuclear-driven. It will carry China's indigenous J-l5 aircraft along with other planes, he added.

Beijing's forces have been involved in sometimes tense confrontations with Japanese and Philippine units over maritime disputes in the East China Sea and South China Sea respectively, prompting fears that the disputes could result in armed clashes.

Beijing claims almost all the strategically vital South China Sea, even waters close to the coasts of other states, and has turned a series of reefs and outcrops in disputed waters into artificial islands capable of hosting military facilities.

In recent months, US ships and planes have approached the new islands to assert international rights to freedom of navigation, with a B-52 bomber on one occasion unintentionally flying within two nautical miles of one of them.